Technical Field
The disclosure relates to a bonding structure and a method of fabricating the same, and more particularly to a bonding structure in which the reliability of the bonding structure is enhanced and a method of fabricating the same.
Background
As the requirement on the complexity and precision of an integrated circuit design continues to increase, various techniques for reducing the feature size of a semiconductor device and/or increasing the integration of an integrated circuit are being explored. The fabrications of high-density metal interconnect and three-dimensional integrated circuits (3D-IC) have been proven to be feasible approaches for upgrading the integration density and improving the performance of semiconductor products.
Conventionally, copper are used in conductive lines for connecting semiconductor devices to a substrate or bonding metal for stacking chips or wafers to achieve 3D-IC configurations. However, the application of these metal bonding structures suffers some adverse challenges which are yet to be overcome.
FIG. 1 is a schematic cross-sectional view illustrating a conventional bonding structure. Referring to FIG. 1, the bonding structure 100 mainly includes a first substrate 110 and a second substrate 120. The first substrate 110 includes a first bonding element 112 disposed thereon. Likewise, the second substrate 120 includes a second bonding element 122 disposed thereon. The first and the second bonding elements 112, 122 are composed of a metal, such as copper. As a bonding process is performed on the substrates 110 and 120, the first and the second bonding elements 112 and 122 are bonded together, such that the first substrate 110 is connected to the second substrate 120. Alternatively, an adhesive film 130 may be formed between the first and the second substrates 110, 120, enclosing the bonding structure.
As shown in FIG. 1, after the bonding process, the resulting bonding structure remains exposed to the ambient environment, such as air, or in contact with the adhesive film 130, which frequently causes damages to the bonding structure. A formation of a nonconductive oxide film on the surface of the bonding structure may also occur, and the presence of the nonconductive oxide film would lead to a high contact resistance in the device. Moreover, when integration increases, stress-induced voiding and electromigration often happen, especially in an exposed metal surface; hence, device failure is resulted. Further, as the feature size of a bonding pad or a contact becomes smaller and the level of interconnections continues to increase, the above-mentioned problems affecting a bonding structure become even more significant. Ultimately, the reliability of the bonding structure and the final device are impacted negatively.